Influence of May Atlantic Ocean initial conditions on the subsequent North Atlantic winter climate (original) (raw)
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Quarterly Journal of The Royal Meteorological Society, 2003
Lead–lag Maximum Covariance Analysis (MCA) between National Centers for Environmental Prediction re-analysis sea surface temperature (SST) and 500 hPa geopotential-height fields shows that autumn tropical Atlantic SST anomalies are significantly linked with the following-winter North Atlantic Oscillation (NAO). The ability of the Météo-France atmospheric general circulation model ARPEGE to reproduce this relationship is tested, by forcing it with autumn tropical SST anomalies derived from lead–lag MCA analysis results. The autumn SST forcing induces a strong wave-like simultaneous response in October and November. The occurrence of the autumn weather regimes is also affected, in agreement with the significant spatial correlation of the midlatitude part of the wave response with the NAO pattern. By coupling the model with a slab ocean in midlatitudes, we show that the thermal coupling between the ocean and the atmosphere allows a better representation of the midlatitude part of the response. A negative autumn tropical SST anomaly triggers an interaction between the midlatitude SST, the low-frequency circulation and the storm-track activity, which reinforces and maintains a positive phase of the NAO until winter. Copyright © 2003 Royal Meteorological Society
Seasonal Predictability of the East Atlantic Pattern from Sea Surface Temperatures
PLoS ONE, 2014
This study analyzes the influence of sea surface temperatures (SSTs) on the second mode of atmospheric variability in the north Atlantic/European sector, namely the East-Atlantic (EA) pattern, for the period 1950-2012. For this purpose, lead-lag relationships between SSTs and the EA pattern, ranging from 0 to 3 seasons, were assessed. As a main result, anomalies of the EA pattern in boreal summer and autumn are significantly related to SST anomalies in the Indo-Pacific Ocean during the preceding seasons. A statistical forecasting scheme based on multiple linear regression was used to hindcast the EAanomalies with a lead-time of 1 to 2 months. The results of a one-year-out cross-validation approach indicate that the phases of the EA in summer and autumn can be properly hindcast.
The dependence of medium range northern Atlantic Ocean predictability on atmospheric forecasts
Journal of Operational Oceanography
The Mercator-Ocean system provides a weekly analysis and a 14-day forecast of the ocean using a I 13° North Atlantic model assimilating satellite altimetry and in situ temperature and salinity profiles. The model system makes use of the European Centre for Medium Range Weather Forecasting (ECMWF) I 0-day operational forecast for atmospheric forcing. The ECMWF monthly ensemble atmospheric forecast allows an extension to one month ocean forecasts. This paper examines the impact of forcing with these two different atmospheric models on ocean forecast skill. Results show an equivalence of the 7-day ocean forecast with the two different atmospheric data sets and an improvement of the 14-day ocean forecast using the ECMWF ensemble mean output. 28-day ocean forecasts using the ECMWF ensemble output are always better than persistence with significant correlation; especially between forecast sea surface temperature (SST) and best estimate SST.
Summer interactions between weather regimes and surface ocean in the North-Atlantic region
2010
This study aims at understanding the summer ocean-atmosphere interactions in the North Atlantic European region on intraseasonal timescales. The CNRMOM1d ocean model is forced with ERA40 (ECMWF Re-Analysis) surface fluxes with a 1-h frequency in solar heat flux (6 h for the other forcing fields) over the 1959-2001 period. The model has 124 vertical levels with a vertical resolution of 1 m near the surface and 500 m at the bottom. This ocean forced experiment is used to assess the impact of the North Atlantic weather regimes on the surface ocean. Composites of sea surface temperature (SST) anomalies associated with each weather regime are computed and the mechanisms explaining these anomalies are investigated. Then, the SST anomalies related to each weather regime in the oceanforced experiment are prescribed to the ARPEGE Atmosphere General Circulation Model. We show that the interaction with the surface ocean induces a positive feedback on the persistence of the Blocking regime, a negative feedback on the persistence of the NAO-regime and favours the transition from the Atlantic Ridge regime to the NAO-regime and from the Atlantic Low regime toward the Blocking regime.
The atmospheric response to North Atlantic SST anomalies in seasonal prediction experiments
Tellus A, 2003
Seasonal forecasts performed over a 26 yr period as part of the Historical Seasonal Forecasting Project (HFP) are used to analyze the influence of North Atlantic sea surface temperature (SST) anomalies on the atmospheric circulation, its seasonality, and model dependence. The signals related to the El Niño events are first removed from both the SST and the atmospheric data. The North Atlantic SST and the ensemble mean forecast are then correlated over the 26 yr to identify the model response to the SST forcing. The signal-to-noise ratio shows that in spring there is a significant forecast signal that is related to the SST anomaly in the North Atlantic. In that season the two models used in the HFP yield responses to the SST anomaly that are both similar to each other and to the observed response. For the other seasons the agreement between the responses and the observed atmospheric anomalies is poor. In winter the response is very sensitive to the model used.
The Physical Basis for Predicting Atlantic Sector Seasonal-to-Interannual Climate Variability*
Journal of Climate, 2006
This paper reviews the observational and theoretical basis for the prediction of seasonal-to-interannual (S/I) climate variability in the Atlantic sector. The emphasis is on the large-scale picture rather than on regional details. The paper is divided into two main parts: a discussion of the predictability of the North Atlantic Oscillation (NAO)—the dominant pattern of variability in the North Atlantic—and a review of the tropical Atlantic prediction problem. The remote effects of El Niño are also mentioned as an important factor in Atlantic climate variability. Only a brief discussion is provided on the subject of South Atlantic climate predictability. Because of its chaotic dynamical nature, the NAO and its related rainfall and temperature variability, while highly significant over Europe and North America, are largely unpredictable. This also affects the predictive skill over the tropical Atlantic, because the NAO interferes with the remote influence of El Niño. That said, there ...
Re-emergence of North Atlantic subsurface ocean temperature anomalies in a seasonal forecast system
Climate Dynamics, 2019
A high-resolution coupled ocean atmosphere model is used to study the effects of seasonal re-emergence of North Atlantic subsurface ocean temperature anomalies on northern hemisphere winter climate. A 50-member control ensemble is integrated from 1 September 2007 to 28 February 2008 and compared with a parallel ensemble with perturbed ocean initial conditions. The perturbation consists of a density-compensated subsurface Atlantic temperature anomaly corresponding to the observed subsurface temperature anomaly for September 2010. The experiment is repeated for two atmosphere horizontal resolutions (~ 60 km and ~ 25 km) in order to determine whether the sensitivity of the atmosphere to re-emerging temperature anomalies is dependent on resolution. A wide range of re-emergence behavior is found within the perturbed ensembles. While the observations seem to indicate that most of the re-emergence is occurring in November, most members of the ensemble show re-emergence occurring later in the winter. However, when re-emergence does occur it is preceded by an atmospheric pressure pattern that induces a strong flow of cold, dry air over the mid-latitude Atlantic, and enhances oceanic latent heat loss. In response to re-emergence (negative SST anomalies), there is reduced latent heat loss, less atmospheric convection, a reduction in eddy kinetic energy and positive low-level pressure anomalies downstream. Within the framework of a seasonal forecast system the results highlight the atmospheric conditions required for re-emergence to take place and the physical processes that may lead to a significant effect on the winter atmospheric circulation.
North Atlantic forcing of climate and its uncertainty from a multi-model experiment
Quarterly Journal of The Royal Meteorological Society, 2004
To understand recent climate change in the North Atlantic region and to produce better climate forecasts with uncertainty estimates it is important to determine the atmospheric ‘response’ to Atlantic sea-surface temperature (SST) forcing. There have been conflicting results regarding the strength, character and tropical-versus-extratropical origin of this response. For model-based studies, this may indicate differing sensitivities to Atlantic SST, but the comparison is complicated by changes in experimental design. Here, a highly controlled experiment with five atmospheric models is undertaken. The influence of realistic (if reasonably strong) and optimally chosen North Atlantic (equator to 70°N) SST anomalies is isolated. Unexpected global agreement between the models is found (e.g. the North Atlantic Oscillation (NAO), Eurasian temperatures, rainfall over the Americas and Africa, and the Asian monsoon). The extratropical North Atlantic region response appears to be associated with remote Caribbean and tropical Atlantic SST anomalies, and with local forcing. Some features such as the European winter-temperature response would be stronger than atmospheric ‘noise’ if the prescribed SST anomalies persisted for just two years. More generally, Atlantic air–sea interaction appears to be important for climate variability on the 30-year timescale and, thus, to be important in the climate-change context. The multi-model mean response patterns are in reasonable agreement with observational estimates, although the model response magnitudes may be too weak. The similarity between their responses helps to reconcile models. Inter-model differences do still exist and these are discussed and quantified. © Crown copyright, 2004.